Frequency of Incomplete Atypical Femoral Fractures in Asymptomatic Patients on Long-Term Bisphosphonate Therapy

The purpose of our study was to determine the frequency and imaging features of atypical femoral fractures in a consecutive asymptomatic patient population on long-term bisphosphonate treatment and search for distinguishing clinical and laboratory parameters in the subset of patients with fractures. Two hundred femoral radiographs in 100 asymptomatic patients (93 women and seven men; age range, 47-94 years; mean age, 69.3 years) were prospectively reviewed by two radiologists. All patients had received bisphosphonate treatment for at least 3 years and had no history of pain or recent trauma. MRI studies were performed when a fracture was suspected on radiographs. Bone mineral density, serum calcium, albumin, 25-hydroxy vitamin D, intact parathyroid hormone (iPTH), serum C-telopeptide, and urine N-telopeptide values were obtained. Two of 100 patients (2%) had three insufficiency fractures. Both patients, 50 and 57 years old, were white, active, and had been receiving bisphosphonate therapy for 8 years. The patient with bilateral atypical femoral fractures showed typical features of bisphosphonate-related incomplete atypical femoral fractures. MRI confirmed the radiographic findings in both patients. The two patients with incomplete atypical femoral fractures were significantly younger than those without atypical femoral fractures. There were no significant differences among the fracture and nonfracture groups in terms of clinical or laboratory results, except for mean iPTH, which was significantly decreased in the fracture group. The 2% frequency of incomplete atypical femoral fractures in asymptomatic patients on long-term bisphosphonate therapy is higher than suggested in the literature. Aside from age and mean iPTH, there were no significant differences in clinical or laboratory data between the two groups.